Make sure that the method getColumnClass(int) of your table's TableModel
returns Icon.class (or ImageIcon.class) for the column that's supposed
to hold an image. Swing automagically takes care of rendering the image.
[Of course, the getValue(int,int) method of the table model must return
an Icon instance (or ImageIcon instance) for that column.]

Example:

MyTableModel myTableModel = new MyTableModel();
JTable myTable = new JTable();
myTable.setModel(myTableModel);

class MyTableModel extends AbstractTableModel {
    public Class getColumnClass(int column) {
        switch (column) {
            case NAME_COLUMN:
                return String.class;
            case IMAGE_COLUMN:
                return Icon.class;
            default:
                return Object.class;
    }
    public Object getValueAt(int row, int column) {
        // return an Icon if column==IMAGE_COLUMN
        ...
    }

    // ... other methods
}